An address strangers still pay
Start with block zero. Bitcoin’s first block carries a timestamp of January 3, 2009 and pays its 50 BTC reward to a bare public key, and if you put that key through the steps in the Bitcoin developer reference (two hashes, a version byte, a checksum, then Base58 encoding) you get 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa. That calculation was rerun for this entry and matched.
Coins keep arriving there. At 05:28 UTC on November 9, 2026, explorer mempool.space showed that the address had received 57.70763368 BTC across 83,448 outputs in 67,472 separate transactions, and that not one of those outputs had been spent. Nobody asked permission to send. Anybody can read the total, which is exactly what “public” means here.
Telling the formats apart
Most formats give themselves away in the opening characters, which is handy when a supplier pastes one into an email.
| Starts with | Network and type | Defined in |
|---|---|---|
| 1 | Bitcoin, pay-to-public-key-hash (legacy) | Bitcoin developer reference |
| 3 | Bitcoin, pay-to-script-hash | BIP 13 |
| bc1q | Bitcoin, native SegWit | BIP 173 |
| bc1p | Bitcoin, Taproot (SegWit version 1) | BIP 350 |
| 0x plus 40 hex characters | Ethereum and other EVM networks | EIP-55 checksum |
| T, 34 characters long | TRON | TRON developer docs |
A checksum guards most of them against typos. The Bech32 checksum behind bc1q addresses, specified in BIP 173, guarantees it will catch any error touching up to four characters, and EIP-55 puts the chance that a mistyped Ethereum address still passes at 0.0247%. That Ethereum checksum lives entirely in the mix of capital and small letters, so an address written all in lowercase carries none.
TRON’s developer documentation adds a twist. The 20 bytes after its 0x41 prefix are identical to the Ethereum address derived from the same public key. Our address checker redoes this checksum math for an address someone hands you, before any money goes out.
Address, public key and private key
People often treat the three as one thing, and they shouldn’t. The private key signs transactions. A public key is computed from it, and the address is a further step. On Bitcoin it is a hash that “shortens and obfuscates the public key,” in the words of the developer guide, while ethereum.org’s accounts page says an Ethereum address is the last 20 bytes of the public key’s Keccak-256 hash with 0x in front.
Neither step runs backward. Publishing an address on an invoice reveals nothing that could move the coins.
What it does reveal is history. The Bitcoin developer guide warns that reusing one address as a static payment address lets others “easily track the receiving and spending habits” of its owner, including how much they control. The guide’s answer is a new address for each payment you receive.